To assess the efficacy of subcutaneous (SC) efgartigimod PH20 among participants in ADHERE with a time since CIDP diagnosis of <1 year and who had never received CIDP treatment (CIDP treatment-naïve).

Efgartigimod, a human immunoglobulin (Ig) G1 antibody Fc fragment, blocks the neonatal Fc receptor, decreasing IgG recycling and reducing IgGs, which play a role in CIDP pathophysiology. The ADHERE (NCT04281472) and open-label extension ADHERE+ (NCT04280718) trials assessed efficacy and safety of efgartigimod PH20 SC in participants with CIDP.

Participants with active CIDP received weekly efgartigimod PH20 SC 1000 mg (stage-A) for ≤12 weeks. Those with confirmed evidence of clinical improvement (ECI) entered stage-B and were randomized (1:1) to weekly efgartigimod PH20 SC or placebo for ≤48 weeks. Participants with clinical deterioration in stage-B or who completed ADHERE could enter ADHERE+. Primary endpoint of ADHERE stage-A was percentage of participants with ECI. Changes from stage-A baseline to stage-A last assessment in adjusted Inflammatory Neuropathy Cause and Treatment (aINCAT), Inflammatory Rasch-built Overall Disability Scale (I-RODS), and grip strength scores were assessed. Outcomes in CIDP treatment-naïve participants are reported.

Of the 322 participants enrolled in ADHERE, 24 were treatment naïve. During stage-A (≤Week 12), 87.5% (21/24) of treatment-naïve participants had confirmed ECI, compared with 64.8% (193/298) across the remaining ADHERE population; time to initial confirmed ECI (50^th percentile) among treatment-naïve participants was 39.5 (95% CI, 22.0–57.0) days. Improvements exceeding the minimal clinically important difference were reported from stage-A baseline to stage-A last assessment across mean aINCAT (mean [SE] change –1.0 [0.22]), I-RODS (10.7 [2.55]), and dominant hand grip strength (15.3 [3.93]) scores in treatment-naïve participants.

Efgartigimod PH20 SC treatment demonstrated a high level of response rate with quick onset of response in CIDP treatment-naïve participants. These findings address the evidence gap for treatment-naïve patients, an underrepresented population in CIDP research.